Re: [PATCH] config/x86: config support for AMD EPYC processors

[Thomas Monjalon <thomas@monjalon.net>]

17/10/2023 12:27, Morten Brørup:
> > >> From: Tummala, Sivaprasad <Sivaprasad.Tummala@amd.com>
> > >>> From: David Marchand <david.marchand@redhat.com>
> > >>> On Mon, Sep 25, 2023 at 5:11 PM Sivaprasad Tummala
> > >>>> From: Sivaprasad Tummala <Sivaprasad.Tummala@amd.com>
> > >>>>
> > >>>> By default, max lcores are limited to 128 for x86 platforms.
> > >>>> On AMD EPYC processors, this limit needs to be increased to
> > leverage
> > >>>> all the cores.
> > >>>>
> > >>>> The patch adjusts the limit specifically for native compilation on
> > >>>> AMD EPYC CPUs.
> > >>>>
> > >>>> Signed-off-by: Sivaprasad Tummala <Sivaprasad.Tummala@amd.com>
> > >>>
> > >>> This patch is a revamp of
> > >>>
> > >>
> > http://inbox.dpdk.org/dev/BY5PR12MB3681C3FC6676BC03F0B42CCC96789@BY5PR
> > >>> 12MB3681.namprd12.prod.outlook.com/
> > >>> for which a discussion at techboard is supposed to have taken place.
> > >>> But I didn't find a trace of it.
> > >>>
> > >>> One option that had been discussed in the previous thread was to
> > >>> increase the max number of cores for x86.
> > >>> I am unclear if this option has been properly evaluated/debatted.
> 
> Here are the minutes from the previous techboard discussions:
> [1]: http://inbox.dpdk.org/dev/YZ43U36bFWHYClAi@platinum/
> [2]: http://inbox.dpdk.org/dev/20211202112506.68acaa1a@hermes.local/
> 
> AFAIK, there has been no progress with dynamic max_lcores, so I guess the techboard's conclusion still stands:
> 
> There is no identified use-case where a single application requires more than 128 lcores. If a case a use-case exists for a single application that uses more than 128 lcores, the TB is ok to update the default config value.
> 
> > >>>
> > >>> Can the topic be brought again at techboard?
> > >>
> > >> Hi David,
> > >>
> > >> The patch is intended to detect AMD platforms and enable all CPU
> > cores by default
> > >> on native builds.
> 
> This is done on native ARM builds, so why not on native X86 builds too?
> 
> > >>
> > >> As an optimization for memory footprint, users can override this by
> > specifying "-
> > >> Dmax_lcores" option based on DPDK lcores required for their usecases.
> > >>
> > >> Sure, will request to add this topic for discussion at techboard.

This is the summary of the techboard meeting:
(see https://mails.dpdk.org/archives/dev/2023-October/279672.html)

- There is some asks for more than 128 worker cores
- Discussion about generally increasing the default max core count and
trade-offs with memory consumption but this is longer term issue
- Acceptance for the direction of this patch in the short term
- Details of whether it should be for EPYC only or x86 to be figured out
on mailing list

So now let's figure out the details please.
Suggestions?